The ability to maintain a low pressure or vacuum for a prolonged period in a microelectronic package is increasingly being sought in such diverse areas as field emission displays (FEDs), micro-electro-mechanical systems (MEMS), and atomic resolution storage devices (ARS). For example, computers, displays, and personal digital assistants may all incorporate such devices. Both FEDs and ARS devices typically have two surfaces juxtaposed to one another across a narrow vacuum gap. Typically electrons traverse this gap either to excite a phosphor in the case of FEDs or to modify a media in the case of ARS devices.
One of the major problems with vacuum packaging of electronic devices is the continuous outgassing of hydrogen, water vapor, carbon monoxide, and other components of the electronic device. To minimize the effects of outgassing, gas-absorbing materials commonly referred. To as getter materials are typically used. Typically, a separate cartridge, ribbon, or pill that incorporates the getter material is inserted into the electronic vacuum package.
In conventional getter cartridges, the getter material is deposited onto a metal substrate and then activated using electrical resistance, RF, or laser power to heat the getter material to a temperature at which the passivation layer on the surface diffuses into the bulk of the material. Non-evaporable getter material is activated in a temperature range of 250°-900° C., depending on the particular material used.
Getter materials have also been deposited on flat surfaces within vacuum packages. A problem with this approach is that the surface area within the vacuum package that is available for getter deposition is typically limited. At the wafer level, there is a competition between active device area and the area available for getter. To achieve a good vacuum in a sealed package and maintain a low pressure over the lifetime of the device, a high fraction of the surface area inside the package should be getter. Providing a sufficient amount of getter material within the vacuum package is difficult when there is a limited amount of surface area available for getter deposition.
In some conventional vacuum packages, the surface area for getter deposition has been increased by forming an array of columns in a flat surface within the vacuum package. Photolithography techniques are used to define the array of columns. A problem with this approach is that the use of photolithography to define an array of columns increases the complexity and cost of making the package.